chopsis (Peltocaris) primus, all of which reappear in the third fauna. Ceratiocaris, however, occurs in d 5. Aptychopsis (or Peltocaris, Salter, as it more probably is) occurs in the Scotch Upper Llandeilos, whereas in Bohemia it is confined to the base of the Upper Silurians (e 1 and e 2) and to the colonies. similar, if not identical form, however, has recently been discovered by Mr. Lapworth in the Scotch Silurians, high up in the series, and I have found another closely similar form in the sand. stone of the Coniston series (Caradoc) of the north of England.

c. Cephalopoda.-This class of fossils, as is well known, has been an object of M. Barrande's especial study, and his results are, therefore, of the highest value and interest. The Cephalopoda are represented in the colonial fauna by thirty-six species, of which all except species of Cyrtocera are referable to the genus Orthoceras. The Cephalopods, therefore, abounded in the colonial fauna, and this again agrees with the state of things in the earlier portion of the third fauna. On the other hand, bands d5 and d 4, though much thicker than the colonies, have only yielded altogether eighteen species of Cephalopoda, the paucity of these fossils thus contrasting strongly with the abundance of trilobites. It should also be remarked that the small representation of the genus Cyrtoceras in the colonies (only two species being known) contrasts very strongly with the total absence of the genus in the second fauna, and its great abundance in the earlier phases of the third fauna, twenty-six species occurring in e 1, and no less than 201 species in e 2. Lastly, of the thirty-six species of Cephalopoda in the colonies, not one is specifically identical with any form known in the second fauna. On the contrary, thirty-one species reappear on different horizons in the third fauna, the remaining five species being peculiar to the colonies.

d. Pteropodu. Only two species of Hyolithes occur in the colonies, and both reappear in the first phase of the third fauna. Neither occur in d 5, though various other Pteropods occur in this band.

e. Gasteropoda.-Only ten species, belonging to eight genera, have hitherto been found in the colonies (almost all in the Colony d'Archiac). No species is common to the colonies and the second fauna, but the genus Pleurotomaria occurs in both. All the colonial species, however, reappear in the third fauna; and their rarity in the colonies agrees fully with their comparative scarcity in e 1.

f. Brachiopoda.-Only fifteen species of Brachiopods are known in the colonial fauna, and these occur in three colonies only. The brachiopods are, therefore, poorly represented; but the following conclusions may be drawn from such as are present: Firstly, five genera and eight species suddenly occur in the Colony Zippe, in d 4. which band hardly contains anything else but Orthides. Secondly, the colonies contain the genus Spirifer, which is not known at all in the second fauna of Bohemia, and is equally very rare in the Lower Silurian of other countries. The genus, however, is abundantly represented in the first phases of the third fauna. Thirdly, we meet in the colonies with Atrypa reticularis, which is equally unknown in the second fauna of Bohemia, and is comparatively rare in the Lower Silurian series elsewhere. On the other hand, it is a characteristic species of the Upper Silurian series from its base almost to its summit. Fourthly, of the total number of fifteen species, only one is exclusively colonial, and that doubtfully so. Fourteen species, therefore, establish the connexion with the third fauna.

g. Lamellibranchiata.-The most remarkable forms of this class in the colonies belong to the genus Cardiola, the most important species being C. fibrosa, Sow, C. interrupta, Sow, C. gibbosa, Barr., and C. nigrans, Barr. Not one of these species is found in any formation belonging to the second fauna, but all reappear at different horizons in the third fauna.

h. Graptolites. These are very abundant in the colonies, and show many points of affinity with those of the third fauna, whilst they have only few affinities with those of the contemporary phases of the second fauna." Twenty-one species of Graptolites occur altogether in the colonies, and they give rise to the following conclusions:-Firstly, not one species of the colonial fauna can be positively asserted to occur in the second fauna (Lower Silurian). Secondly, fourteen species of the twenty-one reappear in band e 1, and of these six pass on into e 2. There remains seven forms which are peculiar to the colonial zone, and these are found exclusively in the Colony Archiac.

The Graptolites, therefore, contribute largely to establish the connexion between the fauna of the colonies and of the Upper Silurian rocks of Bohemia, no single form being certainly known to be identical in the colonies and the contemporary phases of the second fauna. It is to be noted, however, that the Graptolites of the colonies, as well as those of e 1 and e 2, show upon the whole

most strongly marked affinities with those of the Lower Silurian rocks of Britain and America. This is especially shown by the occurrence of the genera Diplograpsus, Climacograpsus, and Rastrites, none of which is known to be represented in the Upper Silurian of any other country except Bohemia. Not only is this the case, but a large number of the species of Etage E are identical with those of the Caradoc beds (Coniston mudstones) of the north of England, and of similar strata in the south of Scotland. I shall, however, elsewhere endeavour to show that the Graptolites of Bohemia were introduced by emigration from the British

area.

i. Crinoids.-No certain remains of Crinoids have been hitherto detected in the colonial zone, except in one doubtful instance. It should be noticed, however, that Crinoids are very rare in the second fauna, whilst there are several species of Cystideans. On the other hand, crinoidal fragments are extremely abundant in e 1, although the number of specific forms seems to be very small. j. Corals.-Corals have hitherto been found in only one colony, and here there is only one indubitable species, viz., Calamopora (Favosities) alveolaris. As no corals of this group are known in the second fauna, and as they are common in the earlier phases of the third fauna, this establishes another link between the latter and the colonial fauna.

C. RELATIONSHIPS OF THE COLONIAL FAUNA AS A WHOLE.

Regarded as a whole, the following conclusions may be drawn from a study of the fossils occurring in the colonies:

1. Altogether 110 species of fossils are known to occur in the colonies, and although this number is still incomplete, it is to be remarked that the total is little smaller than that of band d 5, in which the colonies are situated, and in which 130 fossil species are known in all. It is a very singular fact, therefore, that these 110 species should be "cantoned" so to speak, amongst 130 species belonging to the older second fauna.

2. The independence of the colonial fauna, in spite of its general connexion with the third fauna is shown by the existence of fourteen species exclusively confined to the colonies. This number indicates the amount of extinction which took place in the interval between the last colony and the definitive appearance of the third fauna in Bohemia. It is to be noticed, also, that it is the

numerically largest families, namely, the Cephalopods and Graptolites which have suffered most in the way of extinction.

3. The colonial fauna is related to the second fauna by no more than four species, all Trilobites, and all found in one colony.

4. On the contrary, the specific connections between the colon ial fauna and the third fauna are represented by ninety-two species, or eighty-three per cent. of the total of colonial species.

5. The same relationships are shown by the general facies of the fossils, irrespective of specific identities. Thus, the last phases of the second fauna are characterised by a predominance of Tri lobites and by the rarity of Cephalopods and Graptolites. On the other hand, the colonies and the first phases of the third fauna were characterised by the rarity of Trilobites and the abundance of Cephalopods and Graptolites.

6. These results lead inevitably to the conception that the species of the colonies have been introduced into Bohemia by migration from a foreign area. This conception becomes more certain by a comparison of the colonial fauna with the Silurian fauna of other countries, by which it appears that many colonial species existed in the Lower Silurian series of the British area, that is at a period earlier than the date of their appearance in Britain.

V. PALEONTOLOGICAL RELATIONS BETWEEN THE COLONIAL FAUNA AND THE SILURIAN FAUNA OF BRITAIN.

The connexions between the Silurian fauna of Britain and Bohemia are two-fold, direct and indirect. The direct connexions are shown by the fact that several of the colonial species of Bohemia are found existing in Britain in the "second fauna," i. e. in the Lower Silurian period. The indirect connexions consist in the fact that some of the Lower Silurian species of Britain are found in Bohemia, not in the colonies, but in the third fauna, i. e̟. in the Upper Silurian period.

The following table shows the number of species which are common to the Lower Silurian of Britain, the colonies, and the Upper Silurian of Bohemia, but which are wholly wanting in the Lower Silurian (second fauna) of Bohemia :

Chierurus bimucronatus, Murch.

Sphære.cochus mirus, Beyr.

Atrypa reticularis, Linn.

Strophomena (Leptæna) euglypha, Dalm.

Cardiola interrupta, Sow.

Graptolites lobigerus, McCoy. (= G. Becki, Barr.)

Nilssoni, Barr.

priodon, Barr.

Bohemicus, Barr.

colonus, Barr.

Roemeri, Barr.

Rastrites peregrinus, Barr.

To these I may add, Climacograpsus teretiusculus, His., Graptolites turriculatus, Barr., G. Sedgwickii, Portl., Diplograpsus folium, His., and Diplograpsus palmeus, Barr.

Of the above eleven species enumerated by M. Barrande as common to the colonies and the Lower Silurians of Britain, six reappear in the Upper Silurian of Britain, and all are found in the third fauna (Upper Silurian) of Bohemia. M. Barrande, therefore, concludes that these species play the same part of precursors in the two countries compared; and he believes that a common centre of diffusion for these species must have existed somewhere between Britain and Bohemia. It should be remarked, however, that of the above eleven species, four of the Graptolites (viz. G. lobigerus, G Nilssoni, G. Bohemicus, and Rastrites peregrinus) are not known, as erroneously believed by M. Barrande, to occur in the British Upper Silurian series; nor are any of the five species added by myself to the above list. It should also be noticed that there is great doubt as to the propriety of the introduction of Cardiola interrupta into the above. list as occurring in the Lower Silurian in Britain. On the contrary, it is becoming extremely probable that all the rocks in which this fossil occurs in Britain are truly of Upper Silurian

age.

The following table shows the species of fossils which are found in the third fauna of Bohemia (Upper Silurian), but which existed at an earlier date in the Lower Silurian of Britain :

Crustaceans.

Calymene Blumenbachii, Brongn.
Staurocephalus Murchisoni, Barr.

Cephalopods.

Orthoceras annulatum, Sow.